Patent GB-483365-A (GB)
Title: Electro-mechanical differential apparatus for comparing electric currents in two similar circuits
IPC: G01R19/10
Filed: 1936-07-15
Abstract: 483,365. Electric signalling and control systems. SOLER, J. July 15, 1936, No. 19689. [Classes 40 (i) and 118 (ii)] [Also in Group XXXVI] An arrangement for measuring, controlling, or indicating the values of electric resistances, currents, voltages or capacities, or for measuring or comparing physical effects or conditions which are extraneous to but modify one of such electrical values, comprises two relaxation oscillator circuits which include the electric values to be compared and which oscillate at frequencies determined by these values, whereby impulses are generated in each circuit which after amplification serve to control one member of a three-part differential mechanism, the third member of which drives an indicator or control member, and moves in accordance with the difference between the two frequencies generated. The oscillator circuits comprise condensers 4, 4<1>, which are charged through resistances from separate batteries or from a common battery 1 and discharged through discharge lamps 3, 3'. At each discharge an impulse is produced which is amplified by the amplifiers 14, 14<1> and causes an electromagnet 42, 42<1> to attract its armature which steps on a part 35, 35<1> of a differential mechanism. The third part 36 of the differential mechanism moves proportionally to the difference between the frequencies generated so that by adjusting the frequency of one of the circuits to be equal to that of the other it is possible to compare or measure any one of the components of the circuit which determine its frequency of oscillation, other components in the two circuits being equal. The part 36 of the differential may operate contacts which effect any desired control. The apparatus may be applied to locating an aeroplane by using two microphones fixed to a rotatable shaft. The output from each microphone is fed into each oscillator circuit and thus causes the oscillation frequency to vary. The microphones are adjusted until each picks up the same volume of sound, this being indicated by equal frequency of oscillation of the two circuits which is shown by the part 36 of the differential remaining stationary. The direction of the aeroplane then bisects the angle between the microphones. In a modification, the microphone 27 rotates continuously, supplying current through an amplifier 34 first to one circuit B and then to the other circuit B<1> through the commutator 19 and brushes 20, 21, 22. The brushes are carried by the third member 36 of the differential so that they are automatically adjusted until the frequencies of the two circuits are equal. In this position the plane through the brushes and the axis of the microphone is at right-angles to the direction of the aeroplane. The apparatus may be used for comparing in this way anything which can control the current in the oscillator circuits ; for example, the current can also be controlled by thermionic valves, photo-electric cells or by devices external to the circuit itself, as well as by the actual components of the circuit.